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WIKI
::
A
 
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formal
system
strong
><
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is
used
for
inferring
theorems
from
axioms
according
to
a
set
of
rules
. 
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Each
formal
system
uses
primitive
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a
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font
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family
:
sans
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;
background
:
none
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text
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decoration
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:
none
;
color
:
#
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;"
title
="
Symbol
(
formal
)"
href
="
https
://
en
.
wikipedia
.
org
/
wiki
/
Symbol_
(
formal
)">
symbols
a
><
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;">(
which
collectively
form
an
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><
a
class
="
mw
-
redirect
"
style
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font
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;
background
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none
;
text
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decoration
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color
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;"
title
="
Alphabet
(
computer
science
)"
href
="
https
://
en
.
wikipedia
.
org
/
wiki
/
Alphabet_
(
computer_science
)">
alphabet
a
><
span
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;">)
to
finitely
construct
a
span
><
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-
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;"> 
span
><
a
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="
font
-
family
:
sans
-
serif
;
background
:
none
;
text
-
decoration
-
line
:
none
;
color
:
#
0b0080
;"
title
="
Formal
language
"
href
="
https
://
en
.
wikipedia
.
org
/
wiki
/
Formal_language
">
formal
language
a
><
span
style
="
color
:
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font
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;"> 
span
><
span
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font
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;">
from
a
set
of
span
><
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color
:
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font
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-
serif
;"> 
span
><
a
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="
font
-
family
:
sans
-
serif
;
background
:
none
;
text
-
decoration
-
line
:
none
;
color
:
#
0b0080
;"
title
="
Axiom
"
href
="
https
://
en
.
wikipedia
.
org
/
wiki
/
Axiom
">
axioms
a
><
span
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;">
t
through
inferential
span
><
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style
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:
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;
font
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family
:
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;"> 
span
><
a
class
="
mw
-
redirect
"
style
="
font
-
family
:
sans
-
serif
;
background
:
none
;
text
-
decoration
-
line
:
none
;
color
:
#
0b0080
;"
title
="
Rules
of
formation
"
href
="
https
://
en
.
wikipedia
.
org
/
wiki
/
Rules_of_formation
">
rules
of
formation
a
><
span
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;">. 
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The
system
thus
consists
of
valid
formulas
built
up
through
finite
combinations
of
the
primitive
symbols
—
combinations
that
are
formed
from
the
axioms
in
accordance
with
the
stated
rules
.
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>